Tokkai Hei 7-332141 published by the Japanese Patent Office in 1995 discloses a gasoline engine which is made to perform self-ignition to improve heat efficiency.
In this engine, gasoline fuel is injected into an intake port to form a premixed fuel mixture, and causes self-ignition by compressing the premixed fuel mixture with the high compression ratio of a direct injection diesel engine, i.e., 14 to 20. As self-ignition occurs at plural locations in the combustion chamber, the combustion period can be shortened, even in the case of an fuel mixture having a lean air-fuel ratio, compared with the case where spark ignition is performed. For this reason, running at a lean air-fuel ratio which was impossible in a spark ignition engine can be performed, and fuel consumption can be largely reduced.
This engine is further equipped with a spark plug, and performs spark ignition under running conditions which demand a fuel mixture in the vicinity of the stoichiometric air-fuel ratio, such as running on full load.